(1) Background: The use of social media has become an integral part of adolescents’ daily lives. However, the intensive use of social media can develop into a health-threatening addiction, but unfavourable health consequences can occur even with less use. Social media user groups categorized as no-risk, moderate risk (of developing problematic behaviour), and problematic use were examined with reference to their prevalence, their associations with individual determinants and health, and the increased health risk between groups. (2) Methods: The Finnish nationally representative HBSC data (persons aged 11, 13, and 15, n = 3408) and descriptive and binary logistic regression analysis were applied. (3) Results: Problematic social media use (9.4%) was most common among older age groups, and among persons with moderate/low school achievement, low health literacy, and low parental monitoring. Belonging to a moderate risk group (33.5%) was most frequent among girls, and among adolescents with low/moderate parental monitoring and health literacy. All the negative health indicators systematically increased if the respondent belonged to a moderate risk or problematic use group. (4) Conclusions: The study confirmed the association between problematic social media use and negative health outcomes and highlighted the need to pay close attention to adolescents at moderate risk who exhibited negative health outcomes.

The findings indicate that loneliness is a major risk to the health and well-being of school-aged children. The strong association between loneliness and SHCs highlights the importance of active preventive actions to reduce loneliness.

Positive mental health is central to adolescent well-being. The present study examines the prevalence of loneliness and positive mental health indicators (mental well-being and self-esteem) in four Nordic countries and associations between loneliness, mental well-being, and high self-esteem. This study is based on data from the Health Behaviour in School-aged Children (HBSC) study which was conducted in 2018 in Denmark, Finland, Iceland, and Sweden. Participants were 5883 15-year-old boys and girls. To examine the associations between loneliness, mental well-being, and self-esteem, structural equation modeling (SEM) was applied. In the comparison of Nordic countries, the prevalence of loneliness was highest among Finnish and Icelandic adolescents. High mental well-being and high self-esteem were most prevalent in Denmark and Sweden. In general, boys scored higher on positive mental health indicators and girls on loneliness. Loneliness was also a strong indicator of low mental well-being and low self-esteem in all Nordic countries. Loneliness is not only associated with mental health problems such as anxiety and depression, but it is also a risk factor for adolescents’ positive mental health. Positive mental health is important for healthy maturation and there is a need to develop initiatives to reduce adolescent loneliness and so support positive development.

The purpose of the study was to examine the trends between 2002 and 2018 in school pressure and school satisfaction among 15-year-old students, across countries and by gender, in the WHO European region and North America, and explore whether there are variations between countries and by gender in the co-occurrence of school pressure and school satisfaction. Methods: Data from the 32 countries that participated in the Health Behaviour in School-aged Children study (HBSC) study between 2002 and 2018 were used. Statistical analyses included ttests, binary logistic regression analyses, and chi-square tests, as required by each of the study aims.Results: School satisfaction tended to increase over the period 2002e2018 among boys, whereas school pressure increased among girls. Also, gender differences tended to dissipate in school satisfaction and generally increase in school pressure. The co-occurrence of school satisfaction and school pressure in 2017/2018 shows that the majority of students are found in the "not pressured enot highly satisfied" and "pressuredenot highly satisfied" groups. There were more boys in the former group and more girls in the latter group. Conclusion: Few students in the 32 countries belonged to the "not pressuredehighly satisfied" group, which from a public health perspective may be seen as the most desirable group. The IMPLICATIONS AND CONTRIBUTIONThis study revealed two predominant trends: school satisfaction tended to increase among boys, and school pressure increased among girls. Few students belonged to the "not pressured-highly satisfied" group in 2017/ 18. There was variability across countries, but no clear patterns associated to geographical location or differences in educational systems were apparent. Conflicts of interest:The authors declare that they have no conflict of interest to disclose. There are no prior publications or submissions with any overlapping information. Disclosure: This supplement was supported by the World Health Organization European Office and the University of Glasgow. The articles have been peer-reviewed and edited by the editorial staff of the Journal of Adolescent Health. The opinions or views expressed in this supplement are those of the authors and do not necessarily represent the official position of the funder.

Aims: Loneliness is an important public health challenge for all ages. This study reports time trends of loneliness among adolescents over a 12-year period and analyses the strength of the associations between loneliness, health complaints, and medicine use. Methods: Data were derived from the cross-sectional Finnish Health Behaviour in School-aged Children study conducted in 2006, 2010, 2014, and 2018. The study population is based on a random sample of schools with 20,444 participants aged 11–15 years. The trends were analysed with a Mantel–Haenszel test, and the strength of the associations was evaluated by mixed-effects logistic and linear regressions. Results: An increasing prevalence in frequent loneliness (2006: 11%; 2018: 15%) was evident over the 12-year study period, especially in girls and 15-year-olds. Among all adolescents, loneliness was associated with a higher risk of recurrent health complaints and medicine use to treat the corresponding health issues, especially nervousness (odds ratio 5.8) and sleeping difficulties (odds ratio 7.6). Conclusions: Adolescence is a period of higher risk of frequent loneliness and associated health complaints. In this study, loneliness was common among adolescence and an increasing trend of loneliness was observed between 2006 and 2018. Also, psychosomatic health complaints and medicine use were strongly associated with loneliness. Persistent loneliness is a significant health risk and failure to resolve loneliness before entering adulthood may imply significant concerns for future well-being.